1. Field of the Invention
The present invention relates to an electronic endoscopic apparatus including an endoscopic scope for mounting a slid-state imaging device and an image processing processor for executing predetermined image processing on an image signal from the endoscopic scope.
Priority is claimed on Japanese Patent Application No. 2011-156635, filed on Jul. 15, 2011, the content of which is incorporated herein by reference.
2. Description of Related Art
In recent years, advancements in semiconductor technology are making it possible to increase the pixel density of solid-state imaging devices, such as charge coupled devices (CCD) and complementary metal-oxide semiconductor (CMOS) sensors. An electronic endoscope for mounting a solid-state imaging device is not exempt from this trend, and electronic endoscopes with higher precision are being developed.
However, as the pixel density of solid-state imaging devices increases, so does the frequency of the clock signal needed for the image processing. For example, the electronic endoscope has a structure wherein there is some distance between the distal-end part of the endoscopic scope that the imaging element is mounted on and the image processing processor that performs the image processing, making signal deterioration likely on the transmission line between the endoscopic scope and the image processing processor. When the frequency of signals transmitted between the endoscopic scope and the image processing processor increases, signal deterioration is even greater. Leakage of electromagnetic waves due to the flow of high-frequency signals along the transmission line also becomes more noticeable.
As a method of solving such problems, Japanese Unexamined Patent Application, First Publication No. 2001-275956 proposes an electronic endoscopic apparatus. In this electronic endoscopic apparatus, a smoothing circuit is inserted into the output unit of an electronic endoscope, and suppresses high-frequency noise emitted between the electronic endoscope and a processor device.
However, Japanese Unexamined Patent Application, First Publication No. 2001-275956 does not disclose the perspective of synchronization between the endoscopic scope and a monitor. Since solid-state imaging devices are mounted on the endoscopic scope at various angles of view according to the observation target and the intended purpose, the operating frequency and the angle of view are different for each endoscopic scope. Therefore, to display the image taken by the endoscopic scope, the frequency should be converted according to the synchronization signal of the monitor.
However, depending on the relationship between the clock for display and the clock for imaging, the cycle of the endoscopic scope for taking an image of one frame will be slightly different from the cycle of the monitor for displaying an image of one frame, deviation between the phase of the endoscopic scope and the phase of the monitor is gradually increasing. If the deviation between the phase of the endoscopic scope and the phase of the monitor exceeds the time of one frame, the phenomena known as ‘passing’ or ‘frame dropping’ occur.
FIG. 5 is a diagram of the relationship between a one-frame cycle taking an imaging clock as a reference, and a one-frame cycle taking a display clock as a reference. As shown in FIG. 5, there is a slight difference between the one-frame cycle taking an imaging clock as a reference and the one-frame cycle taking a display clock as a reference, and the deviation (D0, D1, D2) between the one-frame cycles is increasing over time.
Meanwhile, monitor is becoming a high-speed as it is becoming a high definition, and the input of a signal to the monitor must satisfy a strict timing standard. Even if the one-frame cycles of imaging and display can be completely matched, when a synchronization signal for display is generated by taking as a reference the clock on the endoscopic scope side that is not compliant with television standards, there is a possibility that an accurate display cannot be achieved on the monitor.